Lockheed Martin Michoud Space Systems
The external tank for the NASA Space Shuttle is fabricated of aluminum and steel alloys, and comprises a liquid hydrogen tank, a liquid oxygen tank, and an intertank structure linking the two together. Numerous chemicals have been used in the manufacturing process since the programs inception in the early 1970s. The Michoud Assembly Facility (MAF) began an active pollution prevention program in 1990 to reuce usage of some of these, and in 1991 the corporation signed up to EPAs 33/50 voluntary reduction program. According to the 1992 Toxic Emission Data Inventory, MAF was a major source of toxic air pollutants. By 1993 MAF focused on replacing ozone-depleting chemicals used in ET insulation, and eliminating TCE used extensively in cleaning, degreasing, and liquid oxygen (LO2) processes.TCE comprised 82% of Michoud Assembly Facilitys (MAFs) 33/50 releases targeted for reduction. In addition, Louisiana Air Toxics Regulations required TCE usage reduction. The first effort was to eliminate a step in the precleaning of the LO2 tank. The second most significant reduction occurred by modifying the process to verify cleanliness of the LO2 tank after final cleaning. This change decreased TCE usage from 5,000 to 5 gallons per validation sequence. Finally, TCE vapor degreasing of aluminum parts and panels was eliminated by reducing the heavy oils on received parts and validating a substitute alkaline cleaning step. Tentative plans to use TCE as a substitute for CFC 113 (an ozone-depleter) as a small component verification solvent were dropped.Pollution Prevention does not occur quickly for processes regulated by the stringent requirements of manned space flight. Chemicals used in External Tank Production are a part of NASAs governing specifications. Chemicals and their use protocols may be changed only after conducting extensive tests, securing many approvals, and processing much paperwork.
Manned Space Systems reported 112,900 lbs/yr of TCE releases to the 1988 TRI. By 1991 this was reduced to 100,400 lbs/yr (air emissions 55,000 lbs/yr). By 1995 air emissions were down to less than 4,000 lbs/yr and overall releases below the 10,000 lbs/yr TRI reporting threshold.TCE is a Class II Toxic Air Pollutant and both a suspected carcinogen and reproductive toxin with a TLV of only 100 ppm. Reducing TCE usage also reduced health and safety risks to employees.
Details of Reductions
Additional Information :
Decommissioning TCE support systems, including vapor degreasers, a distillation unit, carbon absorption units, bulk storage tanks, and ancillary piping, cost about $1 million. Without the TCE reduction, at least that amount would have been required for equipment improvements and air emission controls. MAF also avoided a $50,000 disposal cost when DOW Chemical agreed to take the remaining supply of TCE at no cost. TCE purchase costs were not high due to onsite distillation. Furthermore, operations and maintenance costs of the TCE systems were eliminated.